Further Development of Modified UNIFAC ... - ACS Publications

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Further Development of Modified UNIFAC (Dortmund): Revision and Extension 6 Dana Constantinescu*,† and Jürgen Gmehling*,†,‡ †

DDBST GmbH, Marie-Curie-Straße 10, D-26129 Oldenburg, Germany Industrial Chemistry, University of Oldenburg, D-26111 Oldenburg, Germany

‡

ABSTRACT: For process development and simulation, the group contribution concept can be successfully applied for the estimation of the missing pure component and mixture properties. This concept has the great advantage that only a limited number of group interaction parameters is required. With the support of a company consortium founded 1996 at the University of Oldenburg, the group contribution model modified UNIFAC (Dortmund) for the prediction of phase equilibria and excess properties has been continuously revised and extended. Within the consortium the number of available group interaction parameters has been doubled. At the same time, the reliability of the results was greatly improved, and the range of applicability was extended to ionic liquids, polyethers, and so forth, and systems for which no experimental data are available, e.g., reactive systems. In this paper the group interaction parameters for the sulfur groups sulfones, sulfides, and disulfides are given. Furthermore, the current status of the consortium developments is discussed.

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INTRODUCTION

following combinatorial part is applied in modified UNIFAC (Dortmund):

A reliable knowledge of the real behavior, in particular the phase equilibrium behavior, is of special importance for the development, simulation, and optimization of different processes in the chemical, petrochemical, gas processing, pharmaceutical, food, environmental industry, and so forth. g E-models and equations of state can be applied to calculate the phase equilibrium behavior using binary parameters only. But in most cases at least a part of the required binary experimental data is missing. Then group contribution methods can be successfully applied. After the publication of the group contribution model UNIFAC1 in 1975 different UNIFAC modifications have been proposed to eliminate the weaknesses of original UNIFAC for the prediction of activity coefficients at infinite dilution γ∞ and the temperature dependence (respectively excess enthalpy hE), in particular for asymmetric systems. Modified UNIFAC models were developed at the University of Dortmund (modified UNIFAC (Dortmund))2,3 and at the University of Denmark (Lyngby) (modified UNIFAC (Lyngby)).4,5 To obtain better results for asymmetric systems in both models a different combinatorial part than in original UNIFAC1,6 is used. Based on the proposal of Kikic et al.7 and Thomas and Eckert,8 the © XXXX American Chemical Society

⎛ V V⎞ ln γiC = 1 − Vi′ + ln Vi′ − 5qi⎜1 − i + ln i ⎟ Fi Fi ⎠ ⎝

(1)

where Vi, Fi, and qi are volume/mole fraction ratios, surface area/mole fraction ratios, and the van der Waals surface area of component i. Besides Vi the following volume/mole fraction ratio Vi′ is used: Vi′ =

ri3/4 ∑j r j3/4xj

(2)

where ri is the relative van der Waals volume of component i and x is the mole fraction. Furthermore, in both models temperature-dependent group interaction parameters are Special Issue: In Honor of Kenneth R. Hall Received: February 15, 2016 Accepted: May 3, 2016

A

DOI: 10.1021/acs.jced.6b00136 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

its large range of applicability. With the definition of new groups, the range of applicability was extended to refrigerants, ionic liquids, polyethers, and so forth. Modified UNIFAC (Dortmund) has become an important thermodynamic model for process development.16 With the help of modified UNIFAC (Dortmund) various process alternatives can be compared, separation problems in multicomponent systems can be detected, and suitable solvents for separation processes like extraction, azeotropic, and extractive distillation can be selected. Furthermore, the influence of solvents on chemical equilibrium conversion and flash points of flammable liquid mixtures can be predicted, the fate of a chemical in the environment or working place can be estimated, the construction of residue curve maps is directly possible, and so forth. Since the reliability of the results depends on the quality of the group interaction parameters and the range of applicability mainly depends on the size of the parameter matrix, the continuous extension and revision of the group interaction parameter matrix of modified UNIFAC (Dortmund) is most important. A relevant prerequisite for the further development of predictive methods is the direct access to a comprehensive database. For the further development of modified UNIFAC (Dortmund), the Dortmund Data Bank (DDB) is used. With ca. 7.2 million data tuples stored, DDB17 is the worldwide largest factual data bank for thermophysical properties, when compared with other data banks, e.g., the NIST data bank with ca. 4.8 million data tuples.18 Both data banks are continuously updated. In the case of DDB approximately 250 data sets (approximately 1800 data tuples) are added per working day. For fitting the required group interaction parameters of modified UNIFAC (Dortmund) the available database has been enlarged by systematic measurements of missing data in our

introduced, where in modified UNIFAC (Dortmund) the following expression is used: ⎛ a + b T + c T2 ⎞ nm nm ⎟ Ψnm = exp⎜ − nm T ⎝ ⎠

(3)

where the temperature dependence of the group interaction parameter Ψnm between the functional groups n and m is described using the parameters anm, bnm, and cnm. A full description of the modified UNIFAC model (Dortmund) is beyond the scope of this publication. For the equations and parameters of the modified UNIFAC model (Dortmund) the reader is referred to refs 2 and 9 where a full description is given. Revised and extended versions of this method were published in refs 10−15. In the last years the group contribution method modified UNIFAC (Dortmund) has become a valuable predictive thermodynamic model for the development and simulation of industrial processes, because of the reliable results obtained and Table 1. Thermodynamic Phase Equilibrium Data and Excess Properties Stored in DDB for Nonelectrolyte Systems (February, 2016) type of thermodynamic mixture data VLE (normal boiling points of all components above 0 °C) activity coefficients at infinite dilution, γ∞ excess enthalpies, hE excess heat capacities, cPE LLE SLE (a)zeotropic data

number of data sets (data points) 37 300 (89 000) 22 800 6 400 30 540 55 300 (56 500)

Figure 1. Flow diagram for fitting the required group interaction parameters of the group contribution method modified UNIFAC (Dortmund). B



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Figure 2. Screenshots from the software developed for the simultaneous parameter fit of group interaction parameters for three different group pairs.

The required group interaction parameters were fitted for 984 group pairs using vapor−liquid equilibria (VLE), hE, and γ∞ data stored in the NIST databank.

laboratory. Furthermore, sponsors of the consortium19 provided confidential company data for the development work. Recently, a comprehensive new modified UNIFAC (NIST) parameter matrix, based on the same formulations used for modified UNIFAC (Dortmund), has been published.20 In most cases, the authors used the same main and subgroups and van der Waals properties as in modified UNIFAC (Dortmund).

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FITTING OF MODEL PARAMETERS In the case of modified UNIFAC (Dortmund) the required group interaction parameters are fitted not only to VLE C



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Figure 3. Experimental VLE,28 SLE,29 hE,30 and calculated results obtained from a simultaneous fit to three group combinations simultaneously: 42 (cy-CH2) and 67 (CFCl2), 43 (cy-CH2O) and 67 (CFCl2), 43 (cy-CH2O) and 70 (CF2Cl2).

Figure 4. Experimental31 and calculated results obtained from a simultaneous fit to four group combinations: 2 (CC) and 95 (F−CC), 40 (CF2) and 95 (F−CC), 68 (CF2H) and 95 (F−CC), 65 (CFH) and 95 (F−CC).

Figure 5. Modified UNIFAC (Dortmund) parameter submatrix for refrigerants.

of nonelectrolyte subcritical systems in a wide temperature range.2 Table 1 gives an idea about the current number of mixture data for nonelectrolyte systems stored in DDB, which can be

data as in original UNIFAC, but also to other reliable phase equilibrium data (LLE, solid−liquid equilibria (SLE) of simple eutectic systems, azeotropic data (γ∞), and excess properties (excess enthalpies hE, excess heat capacities cPE) D



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Table 2. Modified UNIFAC (Dortmund) Rk and Q k Parameters Together with the Group Assignments for the Main Groups of Sulfones (No. 56), Sulfides (No. 61), and Disulfides (No. 93) main group 56 sulfone 61 sulfides

93 disulfides

subgroup

no.

Rk

Qk

sample

(CH2)2 SOO CH2SOOCH CH3S CH2S CHS −S−S−

110 111 122 123 124 201

2.6870 2.4600 1.6130 1.3863 1.1589 1.0678

2.1200 1.8080 1.3680 1.0600 0.7480 2.2440

sulfolane 2,4-dimethylsulfolane dimethyl sulfide diethyl sulfide diisopropyl sulfide dimethyl disulfide

used for fitting the required group interaction parameters of modified UNIFAC (Dortmund). Besides these data, DDB17 contains data for systems with supercritical compounds, electrolyte systems, polymers, transport, and PvT properties, etc. While VLE data provide the information about the composition dependence, excess enthalpies deliver the most reliable information about the temperature dependence of the activity coefficients via the Gibbs−Helmholtz equation.21 Information about the dilute range and strong asymmetric systems is taken into account using reliable activity coefficients at infinite dilution. For systems with strong deviations from Raoult’s law often liquid−liquid equilibrium data deliver the required reliable information. For fitting temperature-dependent parameters, supporting data at low and high temperatures are most important. While solid−liquid equilibria of simple eutectic systems provide this information at low temperature, excess enthalpies are used as supporting data at high temperatures (>363 K). Unfortunately, most published excess enthalpy data were measured around room temperature. Therefore, using an isothermal flow calorimeter, more than 1100 hE-data sets at higher temperatures (60−140 °C) were measured in our laboratory. Furthermore, a large number of important data such as VLE (more than 1250 data sets), activity coefficients at infinite dilution, SLE for simple eutectic systems, and so forth were systematically measured for the further development of the modified UNIFAC (Dortmund) model. In a few cases also confidential data provided by our sponsors were used for fitting the required group interaction parameters. The contribution of the different types of data to the objective function F is taken into account with the help of weighting factors wi:

group assignment 1 1 1 2 4 2

(CH2)2SOO, 2 cy-CH2 CH2SOOCH, 2 CH3, 1 cy-CH2, 1 cy-CH CH3, 1 CH3S CH3, 1 CH2, 1 CH2S CH3, 1 CH, 1 CHS CH3, 1 −S−S−

Figure 6. Structure of the subgroups for the main groups of sulfones (No. 56), sulfides (No. 61), and disulfides (No. 93).

Simplex−Nelder−Mead method22 is employed first because of its robustness. Close to the minimum of the objective function F, the regression is continued using the Marquardt method23 which provides a much faster convergence. A flow diagram of the software package is shown in Figure 1.

F = wVLE ∑ ΔVLE + wAZD ∑ ΔAZD + w γ ∞ ∑ Δγ ∞ + w hE ∑ ΔhE + w cpE ∑ ΔcpE + wSLE ∑ ΔSLE + wLLE ∑ ΔLLE

■

(4)

NEW FITTING TOOL FOR GROUP CONTRIBUTION INTERACTION PARAMETERS To be able to obtain the most reliable parameters and to use most of the data stored in DDB for fitting the parameters of the different predictive models, our software package has been rewritten and extended. Besides the general tasks of the fitting procedure described above and illustrated in Figure 1, the current software package allows the simultaneous parameter fit to more than two different group pairs. This possibility allows extending the database, since data sets which previously could not be used, can now be used. Exemplarily this advantage is shown in three screenshots (Figure 2) for fitting the parameters of systems with N-formylmorpholine. The group assignment of this molecule contains three different groups (42, 43, 94, as shown in Figure 2a). With the extended software package the group interaction

For fitting the temperature-dependent parameters simultaneously to the different types of data, a sophisticated software package was developed. With the help of this software package, the components with the desired functional groups can directly be selected, since in DDB the structures of all the components are stored in form of connection tables and can be divided directly into the functional groups. In the next step, the mixture data for the selected components are taken from the Dortmund Data Bank and checked for thermodynamic consistency and plausibility. The software allows also an equal distribution of the data sets over the different binary systems, compositions, temperatures (pressures), and searches for the required pure component properties, such as vapor pressure, enthalpy of fusion, melting temperature, and so forth. For fitting the group interaction parameters of modified UNIFAC (Dortmund), the E



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Table 3. Selected New and Revised Modified UNIFAC (Dortmund) Group Interaction Parameters for the Main Groups of Sulfones (No. 56), Sulfides (No. 61), and Disulfides (No. 93) n

m

anm (K)

bnm

1 1 1 2 2 3 3 4 4 5 5 6 6 7 7 7 9 9 9 11 11 13 13 14 15 16 16 18 18 19 21 22 23 23 25 25 33 42 42 42 42 45 50 52 53 55 56

9 61 93 61 93 61 93 61 93 61 93 61 93 43 61 93 42 56 61 56 61 56 93 56 56 42 56 42 56 56 56 56 42 56 42 56 56 50 52 61 93 56 56 56 56 56 61

488.98 860.51 468.40 324.32 −740.24 454.32 −630.42 629.46 −478.07 1105.94 −367.32 34.79 1216.71 −75.75 1038.30 4878.28 437.74 609.50 1154.43 −1336.2 −1366.59 −209.21 −584.73 190.88 1178.79 324.15 2662.02 268.23 −354.35 −50.84 842.49 262.14 289.08 401.70 207.16 270.24 2459.0 426.64 313.43 509.27 246.35 184.79 271.02 −299.38 912.22 −9.632 200.04

0.0292 −1.9600 −2.5567

cnm (K−1)

−1.2194 −1.3904 −1.6876

−5.4483 −0.9851 −6.3876 −2.7983 −3.9013 −6.2811 6.7742 5.9067 −0.4704

−9.9991 −1.4264 −13.9855 −1.4137 −1.8371 −0.02529 −1.8434

0.3332 × 10−2

0.3640 0.6091 0.7969 −0.8200 −0.7325 0.6918

× × × × × ×

10−2 10−2 10−2 10−2 10−2 10−2

0.2076 × 10−1 0.1774 × 10−1 0.1040 × 10−1

−0.5852 −1.2206

1.1963 0.0911 −0.5337 −1.9006 −0.6847 1.2901 −2.0231 0.5554 0.1979

−6.5000 × 10−5 −0.1600 × 10−2

cmn (K−1)

amn (K)

bmn

226.94 −309.94 2660.16 −156.46 232.90 −388.19 −72.27 −305.27 15.05 1343.95 34.71 641.04 −386.35 717.48 −270.53 −444.62 364.42 −537.41 −921.65 1915.20 2622.04 1163.91 178.50 14.91 1667.89 −198.32 −1780.41 −5894.1 −1838.89 180.81 −313.20 −229.08 −69.60 157.63 223.78 452.30 −271.23 125.39 −30.56 −108.17 1120.89 −76.14 −59.04 359.06 −604.90 125.53 742.31

−0.8893 0.6486 −6.8651

1.0430 0.6691 −2.1649

3.7787 −1.4851 −0.7765 2.1022 3.8038 5.3930 −9.9994 −11.7013 −7.1332

−7.5870 1.4520 5.7197 13.088 −9.6529 −0.0642 0.4139

−0.7438 × 10−15

−0.4653 −0.5986 −0.6859 0.1260 0.1347 0.8390

× × × × × ×

10−2 10−2 10−2 10−1 10−1 10−2

0.8006 × 10−2 −0.1650 × 10−2 0.2730 × 10−1

−0.4274 −0.5826

−1.1810 −0.2455 −0.1325 −3.1028 0.4820 −0.7256 1.0475 0.2892 −4.1234

−0.9690 × 10−3 0.7800× 10−2

group pairs were fitted simultaneously to systems containing components from the important class of refrigerants. With the help of the extended software package, for example, the existing parameter matrix for refrigerants (Figure 5) was distinctly extended. In this submatrix, the defined groups are now available for fluorocarbons, hydrofluorocarbons, hydrochlorocarbons as well as for chlorofluorocarbons, hydrochlorofluorocarbons, and vinylfluoride. Today, the actual refrigerant matrix comprises group interaction parameters for 158 group pairs, as shown in Figure 5. By the way, with the help of the new software package not only the group interaction parameters of modified UNIFAC

parameters (e.g., 42 with 94, 43 with 94) and an additional further functional group, e.g., main group 1 (alkanes) with the specified main group 94, can now be fitted simultaneously to NFM-alkane systems, when the additionally required group interaction parameters between the other groups (1−42, 1−43, 42−43) are already available. Figure 2b) shows the extent of the database (57 VLE, 49 hE, 27 LLE, etc.) which, through this procedure, can be used to fit the required parameters. In Figure 2c) typical VLE and LLE results for the system n-heptane−N-formylmorpholine are shown. Further results of this approach are shown in Figures 3 and 4, where the parameters for three (Figure 3) and four (Figure 4) F



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Figure 7. Experimental34,35 and predicted VLE and hE using modified UNIFAC (Dortmund) for various binary systems with dimethyl sulfide and dibutyl sulfide.

(Dortmund), and original UNIFAC,6 but also the required parameters of the group contribution equations of state PSRK24,25 and VTPR26,27 can be fitted. In the future the consideration of ternary and higher systems should be enabled in the simultaneous parameter fit.

This development was possible by the steady growth of the number of data stored in the DDB, as exemplarily shown in Table 4 for water with cyclic ethers. The revision of the old parameters leads to a distinct improvement of the results. For systems with water and cyclic ethers, the results using the old and the new parameters are shown in Figure 9. The current status of the modified UNIFAC (Dortmund) parameter matrix is shown in Figure 10. Today group interaction parameters for 1721 group pairs are available for 103 main groups. As can be seen, modified UNIFAC (Dortmund) can now even be applied for systems with peroxides, cyclic thioethers, imidazoles, morpholines, pyrroles, acrolein, cycloalkylamines, disulfides, N-formylmorpholine, mercury, polyethylene glycols, pyrazine, ionic liquids,40 etc. This enormous development was only possible with the help of the steadily growing Dortmund Data Bank, the systematic measurement of missing VLE, γ∞, hE, SLE and azeotropic data and the support of more than 50 companies of the company consortium. A comprehensive comparison41 of the results of different UNIFAC methods for 10 360 isothermal VLE data sets is shown in Figure 11, where the percentages of VLE data that can be predicted within a certain error, in this case relative pressure deviation, are shown. Figure 11 shows again the improved results of the modified UNIFAC versions compared to original UNIFAC. As expected, modified UNIFAC (NIST), which is mathematically identical with modified UNIFAC (Dortmund), shows a similar performance. Both models predict approximately 90% of the data within a relative deviation

Further Development of Modified UNIFAC ... - ACS Publications

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